This project will investigate the development of linguistic communication in moderately to mildly mentally retarded individuals and nonretarded children. Particularly important in linguistic communication is the expression and comprehension of speech acts. A speech act is the social function (e.g., promising, asserting, questioning) that a speaker intends his or her utterance to perform. A speaker must choose a linguistic form for the speech act planned on the basis of properties of to context and a listener must decide what speech act the form heard conveys on the basis of its linguistic properties and the context. Previous research (e.g., Abbeduto, 1984, Abbeduto et al., 1986a) indicates that the expression and comprehension of speech acts may be especially problematic for mentally retarded people. One purpose of this project is to continue investigating the problems mentally retarded people have in expressing and understanding speech acts. The questions addressed include (1) What types of contextual and linguistic information are used to express and understand speech acts? (2) Is the source of immature comprehension and expression due to a lack of, or a failure to use, the requisite skills and knowledge? (3) Do the same abilities and knowledge underly the expression and the comprehension of speech acts? Studies of comprehension are proposed in which the contextual and linguistic properties available to subjects are varied in ways known to lead competent listeners to different interpretations of target sentences. Studies of expression are proposed in which the contextual properties available to subjects are varied in ways that lead competent speakers to select different linguistic forms for their speech acts. Several methods for assessing the maturity of speech act expression and comprehension will be employed. Retarded individuals at the developmental levels of 5-, 7-, and 9-years will be compared to nonretarded children matched to them on measures of linguistic, social, and cognitive competence. Matching will be achieved through a combination of subject selection and statistical procedures. This will allow the extent of their impairment in speech act skills to be determined and will aid in the search for its causes. This project will also investigate retarded people's knowledge of the information conveyed through language about their social status and that of others. A failure to recognize the status information contained in language will impair people's acquisition of knowledge about the social system and their place in it.